1. Field of the Invention
The present invention generally relates to a method and system for modeling the behavior of a furnace and, more particularly, to a method and system for modeling a furnace to determine the mass and energy flow rate for each gas stream within the furnace.
2. Description of the Prior Art
In the United States, glass manufacturing furnaces generally fall into three broad classes of furnaces: container glass furnaces, flat glass furnaces, and fiber glass furnaces. The container glass furnaces produce approximately 65 percent of all the glass manufactured in the United States and typically either have an end port design or a side port design. The flat glass furnaces produce about 20 percent of the glass in the United States and mainly employ either a float glass method or an energy and labor intensive flat glass method. The fiber glass and specialty glass furnaces are generally smaller than the other types of furnaces and produce approximately 20 percent of the glass in the United States.
The three types of glass furnaces operate under different conditions. For instance, the temperature profiles within the three types of furnaces are typically different whereby the combustion air and exhaust gases are at different temperatures. The furnaces also differ in the number and configuration of firing ports, the production capability of the furnaces, and the amount of electric boosting.
In view of the different furnace designs and the variations in operating conditions, it has generally been difficult in the industry to theoretically evaluate the performance of a glass furnace. While measurements in a furnace can indicate the performance of the furnace with a given set of operating parameters, a change in a parameter or set of parameters may have a significant impact on the furnace's overall behavior. Since a change in operating parameters may have adverse effects on the furnace and on the refractory, the operating parameters of the furnace should not be changed without a good estimation on how the changes will effect the furnace's behavior. A need therefore exists for a method or system for predicting the behavior of a furnace for a given set of operating parameters and also for a change in the parameters.
A glass furnace produces high concentrations of oxides of nitrogen (NO.sub.x) due to the high combustion temperatures required to melt the glass batch materials As with other industries, the glass industry is being forced by increasingly stringent air quality regulations to reduce the emissions of NO.sub.x. For glass furnaces, available options for NO.sub.x control are generally either very expensive or have the potential to negatively impact the process. For instance, two NO.sub.x control technologies for glass furnaces which result in only moderate reductions in emissions, such as 40 to 50 percent, are oxygen-enriched air staging (OEAS) and low NO.sub.x burners (LNB). While another common technology, namely oxy-fuel systems, can help glass furnaces achieve up to 90 percent reductions in NO.sub.x, oxy-fuel systems are rather expensive. A need therefore exists for a method of achieving high levels of NO.sub.x emissions control in a cost effective manner.
A technology that has not yet been applied to glass furnaces is gas reburning. Gas reburning, in general, is a NO.sub.x control technology which can be used to control emissions from virtually any continuous emission source. Gas reburning is not fuel specific but can be applied to equipment fired with coal, oil, gas, biomass, or waste fuels. Some of the principal applications where gas reburning can effectively be applied are utility boilers, industrial boilers, process heaters, incinerators, furnaces, and kilns. A significant amount of the work in the reburning industry has focused on coal-fired utility boilers where gas reburning has successfully been demonstrated to provide control levels between 60 to 70 percent. The emphasis in reducing emissions in coal-fired utility boilers has been due, in large part, to the need to control acid rain precursors, such as NO.sub.x and SO.sub.2.
The addition of a reburning system to a glass furnace, however, alters the temperature profile within the glass furnace and alters the overall thermal process. Before a glass furnace can be designed to have a reburning system, the effects of the reburning system on various aspects of the glass furnace and on the operation of the glass furnace should be determined. These effects include changes in mass flows within the furnace, the effect on the refractory, the effect on the furnace's life-time, the fuel efficiency of the furnace, the effect on the chemistry within the furnace, and the degree of NO.sub.x reduction. A need therefore exists for a method and system for determining the effects of a given reburning system design on the operation of a glass furnace and for determining the mass and energy for each flow within the furnace.
To improve the efficiency of the glass furnace and to maintain high temperatures in a melter, a heat recovery device will often be used to recover heat from the melter flue gases and to provide high air preheat temperatures. Two common recovery devices are a regenerator and a recuperator. A regenerator comprises a stack of refractory bricks or other packing material which receives the products of combustion and a complementary stack which preheats air for combustion. At regular intervals, such as every 15 to 20 minutes, firing ports in the furnace are reversed with exhaust ports. As a result, the air entering the regenerator is preheated to high temperatures by the heated stack of refractory bricks. A recuperator, in contrast, routes the combustion flue gases to the air-side portion of the furnace in order to transfer the heat from the combustion gases to the air entering the furnace. This heat transfer takes place through a solid separator, so the air and flue gas do not mix. Because a given glass furnace may have either a regenerator or a recuperator, a need exists for a system and method for determining the mass and energy of each flow within a furnace and the temperatures within a furnace having either a regenerator or a recuperator. Since a furnace may also have reburning, a need exists for a method and system for determining the mass and energy of each flow and the temperature profile within a furnace having reburning.